Automatic noise-reduction (ANR) headsets typically include a voice microphone along with two earcups which are worn over the ears of users to enhance or protect their hearing in noisy environments, for example by shielding their ears from loud persistent noises or filtering out background noises that might interfere with speech or music. These headsets include ear speakers, one or more extra microphones, and ANR circuitry. The microphones sense sounds in certain frequency ranges, and the ANR circuitry attempts to cancel or suppress it by driving the ear speakers to vibrate in opposition to the undesired sounds.
Recent years have seen the emergence of in-the-ear (ITE) earphones that incorporate ANR technology. The size and weight constraints with these devices typically force manufacturers to compromise one performance trait in order to enhance another. These tradeoffs ultimately result in a device that is less than optimal.
For example, U.S. Pat. No. 8,682,001 to Annuziato et al. (Annunciato) advises that for adequate ANR functioning, lower acoustic impedance is of prime importance. Moreover, it further states that reduced impedance is best achieved through having a nozzle or port connecting a front cavity portion of the earphone to a user ear canal, with the nozzle not only having as large cross-sectional area as possible, but also having a high aspect ratio (cross-sectional area to length ratio.) To this end, Annunziato provides a nozzle portion of its earbud device that has a cross-sectional area of 10 square millimeters and length of approximately 10 millimeters. Unfortunately, these dimensions force users to trade comfort for effective noise reduction. Moreover, the larger cross-sectional area makes it impractical to use the popular silicone rubber and foam earbud tips that easily conform to various shapes and sizes of user ear canals and ultimately provide a better acoustic seal of the ear cavity and thus better noise reduction.
To avoid use of a wider uncomfortable nozzle, U.S. Pat. No. 8,385,560 to Solbeck et al. (Solbeck) uses a smaller one along with a narrow probe tube that extends between the microphone in the front cavity near the ANR driver (speaker) and the ear cavity. While this approach avoids the uncomfortable nozzle, it also has at least two negative side effects of its own. One side effect is that Solbeck's tube increases the likelihood that the ANR circuitry will become unstable (because of reduced phase margin) and thus create high pitched squeals in the ears of users. The other side effect is that the tube requires added circuitry or processing to adjust frequency response of the ANR circuitry, and this in turn increases the level of electronic noise users experience. These side effects are acceptable for Solbeck's objective of protecting user hearing and allowing basic communication, but not for ITE earphone users who desire a superior music and audio listening experience.
Accordingly, the present inventor has recognize a need for alternative devices that avoid or otherwise reduce the design compromises built into most conventional ITE ANR devices.